Plasmid-mediated drug resistance of shigellae in Kuwait.

Of 153 clinical isolates of shigellae examined, 64.7% belonged to Shigella flexneri, 18.9% to Sh. sonnei, 11.8% to Sh. boydii and 4.6% to Sh. dysenteriae. Part of these isolates were resistant to sulfamethoxazole and streptomycin (88.2% each), ampicillin (66.7%), tetracycline (63.4%) and co-trimoxazole (43.1%), with levels of resistance (MIC50 and MIC90) being invariably high. Resistance to three or more drugs (multidrug resistance) was seen in 77.8% of the isolates. All the 25 strains examined for transfer of resistance contained R-plasmids, both autotransferable and non-autotransferable (mobilized by transfer factor X). The frequency of transfer of different r-determinants varied from 2.7 X 10(-8) to 1.4 X 10(-3).